Shielded loop antenna



Dec. 18, 1945. w: D. MGGUIGAN 2,391,026

SHIELDED LOOP ANTENNA Filed Nov. 15, 1945- 2 Sheets-Sheevl ATTURNE'Y Dec. 18, 1945. 'w. D. McGUlGAN 2,391,026

' SHIELDED LOOP ANTENNA Filed Nov. 5, 1945 2 Sheets-Sheet 2 J 72 42 61 22 a so 5 h n: 4

6'2 79 i 71 41' i 17a I Q2; 5 l

Patented Dec. 18, 1945 SHIELDED LOOP ANTENNA William D. McGuigan, New York, N. Y., assignor to Federal Telephone and Radio Corporation, New York, N. Y., a corporation of Delaware Application November 15, 1943, Serial No. 510,266

8 Claims.

This invention relates to shielded loop antennas and more particularly to shielded loop antennas of the type designed to produce substantially uniform radiation of substantially plane polarized waves. 1

In a copending application of M. Fuchs, Serial No. 509,251, filed Nov. 6, 1943, entitled Shielded loop antenna, a system for supplying energy over asymmetrical dual line to or from an antenna designed to produce substantially uniform radiation of plane polarized waves, is shown. This previously proposed antenna depends in part for its operation on the impedance effect provided by gaps in the outer conductor of an eifective concentric line. The energy is fed to the center conductors of adjacent concentric line sections over a branched dual conductor line. This proposed system avoids unbalance due to unbalanced voltages induced in the antenna from appearing at the translation end of the system but depends on the balanced dual line to provide such coupling.

It is an object of my invention to provide an antenna which will produce the desired uniform radiant acting effect, in transmission or reception of radio waves, and which may be coupled to a translating equipment over an unsymmertical line.

' It is a further object of my invention to provide a relatively simple antenna loop which may be coupled to a concentric conductor line and still produce a substantially uniform radiation pattern of plane polarized waves.

It is a still further object of my invention to provide a loop antenna which is substantially shielded from reception of unbalanced voltages and which may be coupled to an unbalanced translating system over a concentric conductor lead.

With these and other objects in view, a better understanding of my invention may be had from the particular description of an embodiment thereof made with reference to the accompanying drawing, in which:

Fig. 1 is a top plan view partly in section illustrating a structural embodiment of my invention;

Fig. 2 is a schematic circuit plan view used in further explanation of my invention;

Fig. 3 is an elevational view of an antenna such as shown in Fig. 1 shown at a smaller scale;

Fig. 4 is a plan view of a modified form of loop construction in accordanc with my invention;

Fig. 5 is an elevational view of the antenna of Fig. 4; k

Fig. 6 is a plan view of a still further modification of a loop construction in accordance with my invention; and

Fig. '7 is a still further modification showin three radiating elements.

Turning first to Figs. 1 and 2, the antenna includes four radiant acting arms or members l0, II, I2 and I3, formed of hollow conductive material. From the mid-points of each of arms II] to I3 are provided inwardly directed hollow supporting arms I4, I5, I6 and I1, extending inwardly to a common junction indicated by junction box 5. A feed conductor is provided preferably of concentric line type having an outer shield I8 fastened to supporting arms I4, I5, I6 and 11 by means of junction box 5 and serving as a support therefore and an inner lead conductor I9. Arms I0, II, I2 and I3 are arranged to provide a substantially closed geometric figure and the adjacent ends of each of the members are spaced apart a small distance to provide gaps I, 2, 3 and 4, respectively. The width of the gaps may be varied within close limits to control the capacity between adjacent arms, but should be small with respect to the radius of the member. Connected to lead I9 at the common junction point are four conductors 20, 2|, 22 and 23 extending outwardly within hollow arms I4, I5, I6 and I1. These inner conductors are preferably portions of concentric conductor lines such that the inner conductors are arranged symmetrically within the supporting arms. Each of these conductors extends outwardly to the mid-point of the corresponding radiant acting member and from there extends centrally within the hollow radiant acting members, as shown at 24, 25, 26 and 21 in the same direction around the periphery of the loop and across the gap into the next adjacent radiant acting member, as indicated at 30, 3|, 32 and 33.

Turning more particularly to Fig. 2, it can be seen that this arrangement will provide inner conductors in which the instantaneous flow of current around the loop is always in the same direction. As a consequence, the current will be flowing in the inside of the hollow members in the opposite direction and because of the impedance introduced at the gaps current will be flowing in the outer conductors in the same direction as in the inner conductors. The hollow conductive members are made a half wavelength or less in length preferably a length in the order of one-quarter to one-third of a wavelength so ponent to tune the antenna so that the desired impedance characteristic will be obtained.

In order properly to tune the antenna, this reactance must generally be capacitive and since these lines must terminate short of the succeeding conductor, they cannot be over a one-quarter wavelength long. Since a capacitive reactance is generally necessary, the inner conductors arenot connected to the outer shell but are leftin openended relation, providing the desired capacitive reactance at the gaps I, 2, 3 and 4 may be controlled by suitably adjusting the length of each of the conductors 30 to 33, inclusive. With this arrangement, it is clear that the radiant acting members are energized either in reception or transmission to provide a substantially uniform horizontal radiation pattern of substantially pure plane polarization in planes parallel to the plane of the antenna.

The structural arrangement of the various members and supporting arms which will enable ready construction of the loop may take the form shown in Fig. 1. In this form, each of the members In, H, l2 and I3 is composed of two sections ill-4|, 50-5l, Gil-6| and NJ-1| interconnected at their mid-points by junction boxes 42, 52, 62 and 72, respectively. Supporting arms M, I5, I 6 and H are also fastened at their outer ends in the respective junction boxes 42, 52, 62 and i2 and at their common junction point within a junction box 5. The supporting outer conductor I8 is also fastened in junction box as can more clearly be seen by reference to Fig. 3.

It will be seen that the entire structure provides in efiect four loops composed of the sections of the conducting members and the respective arm members. The currents which would tend to radiate from the supporting arms are substan tially compensated since currents from tWo adjacent loops would tend to flow in opposite directions on the two sides of the arms. In the elevational view, as shown in Fig. 3, the antenna 9| may be coupled over the unsymmetrical line l8l9 to a translator unit 92 which may be an unbalanced receiver or transmitter arrangement. This construction therefore, provides a coupling circuit whereby an unbalanced translator may be coupled over an unsymmetrical line to the substantially balanced loop arrangement.

It is clear that the geometric configuration shown in Fig. 1 is merely one example of the loop in accordance with my invention. In Fig. 4 a simla loop is provided with the radiant acting members curved so that the geometric figure produced is substantially circular. In this figure, the elements corresponding to those shown in Fig. l are numbered with the same reference characters but with an added 1 in front thereof. Thus, instead of sections 40, 4|, 42, etc., the numerals applied thereto are MD, MI, |42,etc.

Fig. 5 illustrates an elevational view of the antenna arrangement of Fig. 4 and hows a structural arrangement wherein the supportin arms H4 to H1 are not arranged in the plane of the antenna but at an angle thereto. This same structure may be provided for supporting the loop antenna of Fig. 1, if desired. Thi typ 0 structure has the effect of increasing the rigidity of the antenna as a whole but has the disadvan tage that greater amount of radiation from these supporting arms will occur than in the other arrangement.

In Fig. 6 is shown a still furthe modification of my invention in which the junction boxes are arranged at the corners of the square instead of in the middle thereof and consequently the gaps between the sections of the various radiant acting members occur midway along the sides of the square. In this figure, reference characters with a 2 added in front thereof corresponding otherwise with the reference characters of Fig. 1 are applied to the various sections of the antenna.

Fig. 7 illustrates in plan diagram a circular antenna composed of only three radiant acting members.

While I have shown a few geometric figures to which my invention may be applied, it should be distinctly understood that any desired configuration of the antenna may be used. Furthermore, the supporting arrangement may be varied in many ways, as will be clear to those skilled in the art. The illustrations are merely shown as examples and are not to be constituted as elements of my invention, as set forth in the objects thereof and in the appended claims.

What is claimed is:

1. A radio antenna adapted for radiant action substantially uniformly about said antenna comprising a plurality of hollow conductive radiant acting members, each member being not over a half wavelength long at the operating frequency, said members being arranged in the form of a substantially closed geometric pattern and'being spaced apart a small distance at their adjacent ends, a hollow conductive arm joined respectively to each of the mid-points of the respective conductive members and extending inwardly of said geometric pattern to a common junction, a lead conductor at said common junction, inner conductors in each of said arms each connected at one end to said lead conductor, said inner conductors each extending from the respectiv junctures of said arms and said members within said hollow members in the same direction aroundthe periphery of said geometric pattern and across the gap between adjacent members into the next adjacent hollow member, and terminating short of the succeeding conductor, said conductor in said next adjacent hollow members serving with said members to provide a capacitive reactance between the respective conductor and the conductive members at said gaps.

2. A radio antenna according to claim 1 wherein said arms are arranged substantially in the plane defined by said radiant acting members.

3. A radio antenna according to claim 1 wherein said members are each made less than onethird wavelength long.

4. A radio antenna according to claim 1 furthercomprising a concentric shield about said lead conductor connected to said conductive arms, serving to support said antenna.

5. A radio antenna according to claim 1, wherein each of said conductive members comprises two equal length sections and a conductive'junction box serving to interconnect said separate sections, and to fasten together the respective arms and members.

6. A radio antenna system comprising a plurality of hollow radiant acting members each member being less than a half wavelength long at the operating frequency, said members being arranged in the form of a geometric pattern and being spaced apart a small distance at their adjacent ends to provide gaps, a hollow conductive arm joined respectively to each of the midpoints of the respective conductor members and extending inwardly of said pattern to a common junction, a translator device, and means for coupling said members to said translating device in energy transfer relation comprising an unsymmetric line having one hollow conductor fastened to said common junction, and a second conductor within said hollow conductor extending to said common junction, inner conductors in each of said hollow arms each connected at one end to said second conductor, said inner conductors each extending from the juncture of said arms and said members within said hollow members in the same direction around said periphery and across said gap into the next adjacent hollow member, and terminating short of the succeeding conductor.

'7. A radio antenna system according to claim 6 wherein said conductors are terminated within said next adjacent member at a distance less than a quarter wavelength from said gap in open-ended relation and to provide with the surrounding member a capacitive reactance as seen from said gaps.

8. A radio antenna adapted for radiant action substantially uniformly about said antenna comprising a pluraltiy of hollow conductive radiant acting members, each member being not over a half wavelength long at the operating frequency, said members being arranged in the form of a substantially closed geometric pattern and being spaced apart a small distance at their adjacent ends, a hollow conductive arm joined respectively to each of the mid-points of the respective conductive members and extending inwardly of said geometric pattern to a common junction, a lead conductor at said common junction, inner conductors in each of said arms each connected at one end to said lead conductor, said inner conductors each extending from the respective junctures of said arms and said members within said hollow members in the same direction around the periphery of said geometric pattern and across the gap between adjacent members.

WILLIAM D. MCGUIGAN. 

